When I walked into Child Watch after my Kickboxing Aerobics class, my son, Kung Fu Panda, was enjoying some apple slices (which we call apple boats). I cheerfully told him it was time to go, but this news nearly brought him to tears. Thinking he was just having too much fun, I assured him he could come back on Monday. He blurbled out something about how his friends hadn't arrived yet, and thinking he meant the other boys his age who are often there at the same time, I told him he could play with them another day.

"No," one of the staffers, Ms. Penny, told me, "he is talking about his imaginary friend, Spongebob." This seemed unlikely, since KFP only recently saw his first episode of "Spongebob," at a friend's house.

Finally, as he continued his narrative in the car, the story took shape. He and Ms. Penny had spent most of the hour cooking in the play kitchen, whipping up hot dogs, macs and cheese, and cake. They then set the table, and KFP used a play phone to call up several imaginary friends. Apparently, Buster and Arthur (from the Arthur book series and TV show) showed up right away, along with Bob the Builder. Ms. Penny's friends (whom KFP couldn't recall) also made it. But sadly, Spud and Scruffy (from Bob the Builder) were stuck in traffic on the highway. They hadn't yet arrived when I had walked in to take him home.

KFP was still sniffling: "The food will be wasted."

It was time to jump into the improv pool with both feet. "What were they driving?" I asked.

"Their talking tractor," KFP told me.

"Well, they just arrived. I see them pulling into the tractor parking section around back," I said excitedly.

"The tractor parking is in front, on the grass," KFP deadpanned.

"Yes, of course, that's what I meant."

He insisted on driving past it to be sure. I held my breath as we drove by the grassy lawn, waiting for his next move. "They're here! I see the tractor!" he called.

Together, we described Spud and Scruffy running down the hallway to Child Watch, gulping down the macs and cheese gratefully, sharing the one hot dog that was left, and inhaling the cake.

"I bet they are very happy," I told him.

"I better tell Ms. Penny on Monday that they are here to stay," he mused.